Lubricants are generally employed in metalworking operations. Such operations include rolling, forging, blanking, bending, stamping, drawing, cutting, punching, spinning, extruding, coining, hobbing, swaging and the like. The present invention concerns lubricants for such type of metalworking operations, and in particular such operations as employed in the automotive and appliance applications. In the automotive and appliance fields, the term "forming" is used as a broad term to cover all pressworking operations on sheet metal, which operations may be further categorized as all mechanical processes where sheet metal is formed into specific shapes by the use of mechanical presses. Automotive and appliance formed parts may be produced by one or a combination of three fundamental operations, defined as stamping, shallow drawing and deep drawing. Stamping is further defined as all forming operations where parts are formed from sheet metal where there is no change in the thickness of the sheet metal. Drawing defines all forming operations where there is a change or reduction in thickness of the sheet metal. Shallow drawing forms a shape no deeper than one half its diameter with only small reductions in metal thickness. Deep drawing forms shapes deeper than half its diameter with substantial reductions in metal thickness.
Metalworking lubricants facilitate these operations by reducing friction between the metal being worked and the tooling employed for that process. This reduces the power required for a given operation, the wear of the surfaces of the tooling, and prevents adhesion between the metal being worked and the tooling operating thereon. Lubricants also prevent adhesion between metal pieces during storage, handling or operations. Also, they often provide corrosion protection to the metal being processed. In automotive and appliance applications prevention of adhesion between metal pieces and between such pieces and the work elements is of extreme importance.
In some metalworking processes, including automotive and appliance applications, coils or rolls of steel, in particular cold rolled or galvanized steel sheets, are cut into pieces, called blanks, which are stamped or drawn to produce the desired parts. Such automotive parts formed by stamping or drawing, as these terms are generally used, include fenders, hoods, deck lids, quarter panels, oil pans, fuel tanks, floor panels, inner and outer door panels and the like. Appliance parts, formed by stamping and drawing as these terms are generally used, include washer tops, dryer tops, washer fronts, dryer fronts, top and front lids and dryer tumblers and the like. Prior to the use of lubricants known as prelubes, the normal procedure was to apply an oil at the steel mill to such coils or rolls as a rust preventative prior to shipping to the processing site, such as a stamping plant. Between the steps of cutting the sheets into blanks and stamping or drawing, these rust preventive oils would be removed by cleaning and a drawing lubricant applied to the metal work element immediately before stamping or drawing. These forming lubricants are used to reduce friction and facilitate the metalworking operation.
In recent times the use of separate rust preventive oils and drawing lubricants has been in some instances replaced by the use of a single composition known as a prelube. Prelubes are generally applied at the steel mill during temper rolling or inspection, as would be a rust preventive oil, prior to shipping and are not removed from the metal until after the blanks are cut and the parts formed. Thus the use of such prelubes eliminates the steps of removing the oil and applying a forming lubricant before further working.
Prelubes, therefore, must function as both a rust preventative and forming lubricant. In many instances, and particularly for automotive and appliance applications, a prelube must be removable with alkaline cleaners, be non-staining to the metal, and be compatible with other chemicals utilized in processing the products in question. Thus the use of prelubes eliminates the tedious process of applying and removing the combination of rust preventative oils and forming lubricants before further working with only one composition. Prelubes thus offer a variety of performance benefits in replacing a multitude of products with one composition.
The advantages obtained by using a prelube would be diminished if unusual methods were necessary to remove the lubricant from the final product. In the automotive and appliance fields, alkaline cleaners are the normal compositions employed for cleaning. These aqueous alkaline cleaners are normally mixtures of amines, inorganic alkalais and biodegradable nonionic surfactants. These cleaners are used today, especially in the automotive industry, at operating concentrations of one-two ounces per gallon and at temperatures from 105.degree. to 125.degree. F. Formed parts are cleaned in a variety of system types utilizing spray, immersion and combination of both. Exposure times range from one to three minutes depending on type of part, metal substrate, lubricant and operating conditions of the alkaline cleaner.
There are times where coated steel coils are stored for long periods before use. Some of the coatings ingredients may oxidize during storage. These oxidation products stain steel sheets, particularly mild steel sheets. Hence, industries in which storage periods are long require prelubes that are substantially non-staining and capable of neutralizing any oxidation by-products.
Parts are sometimes formed with severe bends which may entrap some of the lubricant used in the metalworking operation. Although the lubricant may be removed after working from all exposed surfaces, the entrapped portion remains and may be vaporized or otherwise released under subsequent processing conditions. The potential for the release of entrapped lubricant thus requires compatibility between the lubricant and cathodic primers, automotive adhesives and appliance porcelain coatings. Although some parts being formed in a typical stamping plant will not be painted nor come into contact with adhesives, and thus the use of non-compatible lubricants thereon would pose minimal risks, efficiency in the overall operations makes in highly desirable to utilize the same lubricant or prelube throughout the plant.
The prelubes now used commercially in the automotive and appliance industries are liquid hydrocarbon based compositions containing a variety of chemical components. These compositions tend to drain off the metal surfaces, creating maintenance problems. They tend to be or become unevenly distributed on the metal surfaces due to capillary forces or gravity. The properties of corrosion prevention and drawing assistance both depend in significant part on uniformity of lubricant film. The automotive and appliance industries desire a prelube that provides lubricant film uniformity and film strength undiminished during shipping and storage periods. Further, film strength is a particularly significant property for facilitation forming operations; a lubricant having high film strength will permit more severe draws to be made. When hydrocarbon based compositions are used, housekeeping and cleanliness are extremely hard to maintain. They leak onto tooling surfaces, contaminate floor trenches and waste treatment streams, volatilize into the air and may create dermatitis on the press forming personnel. Automotive and appliance industries require forming lubricants that eliminate these problems either through their chemistry of by being compatible with the existing processes.
A lubricant that is effective for the purposes for which it is intended should be low cost and work at low coating weights, e.g., as a thin film. Traditional hydrocarbon base prelubes are used at coating weights ranging from 300 to 1000 mg/ft.sup.2.
To be successful in treating metal for use by automobile manufacturers, it is important the prelube have the property of being easily cleaned and removed by aqueous alkaline cleaners at temperatures as low as 105.degree. F. Also, the prelube must provide good corrosion protection to the part being coated. Furthermore, the prelube must be compatible with the various types of metal substrates used in automotive industry today including cold rolled steel, hot dip galvanized, electro-galvanized and aluminum.
It is an object of the present invention to provide a metalworking lubricant, particularly a solid film prelube, that provides the foregoing desirable characteristics and permits the attainment of the foregoing advantages in the metalworking field, and in particular in the automotive and appliance industries.
It is a further object of the present invention to provide a method of lubricating metal, particularly cold rolled and galvanized steel sheets, prior to stamping and drawing operations, that provides the foregoing desired advantages.
These and other objects of the invention are described below.